1. Field of the Invention
The present invention relates to a manufacturing method of a semiconductor device, and for example, relates to a manufacturing method of a semiconductor device including a process for peeling a pressure sensitive adhesive tape, which has been affixed during a manufacturing process, from semiconductor chips which constitute a stacked MCP (Multi-Chip Package) type semiconductor device and in which an adhesive layer is formed on a rear surface.
2. Related Background Art
Generally in a manufacturing process of a semiconductor device, a semiconductor wafer which has finished with element formation is separated along a dicing line or a chip division line, and broken to be separated into a plurality of semiconductor chips. A pressure sensitive adhesive tape (which will hereinafter be referred to a PSA tape) is affixed to the semiconductor wafer before and after the separation process, and the semiconductor chips in the piece form are integrated to keep a wafer shape. The semiconductor wafer, which has thus been broken into a plurality of semiconductor chips and is supported by the PSA tape, is transferred to a mounting process using a die bonder or the like. Each semiconductor chip separated from the semiconductor wafer is picked up from the PSA tape, and brought to a mounting process such as a process of mounting to a leadframe and a TAB tape or a process of sealing into a package, thereby completing the semiconductor device.
In picking up such individual semiconductor chips the rear surface of the semiconductor wafer, opposite to a surface to which the PSA tape is affixed, is affixed to another PSA tape which is affixed to a wafer ring, and then the PSA tape is peeled off, and the wafer ring is mounted to a pickup device to pick up the individual semiconductor chips.
FIG. 23 is an enlarged sectional view of essential components of a conventional pickup device disclosed in Japanese Patent Publication Laid-open No. 2003-17513 (see FIG. 1, FIG. 2, and parts where explanation is given in connection with these drawings), and it shows an operation for picking up a semiconductor chip 100 from a PSA tape 101.
When the semiconductor chip 100 is peeled off and picked up from the PSA tape 101 affixed to the wafer ring, raising pins (needles) 102 are projected (lifted) via the PSA tape 101 from a rear surface side of the semiconductor chip 100, and elasticity of the PSA tape 101 is utilized to peel off the semiconductor chip 100. The raising pins 102 are disposed at corner portions or positions corresponding to the vicinity of a central portion of the semiconductor chip 100, and their base portions are attached to a pin holder 103.
As an order to peel off the semiconductor chip 100 from the PSA tape 101, a holding table, on which the PSA tape 101 to which the semiconductor chip 100 is affixed is fixed, is first moved so that the semiconductor chip 100 to be picked up will be located above the raising pins 102. Next, for example, detection of a position of the semiconductor chip 100 to be peeled off and mark detection for identification of non-defective/defective products are performed, and an internal portion of a backup holder 104 is attracted by vacuum to cause the PSA tape 101 to be sucked and fixed onto an upper surface of the backup holder 104. In this state, the pin holder 103 to which the raising pins 102 are mounted is lifted to project the raising pins 102 from the upper surface of the backup holder 104 and raise the semiconductor chip 100 via the PSA tape 101 from the rear surface side. The raised semiconductor chip 100 is sucked by a suction collet 105 and supplied to the mounting process.
There has recently been a keen desire for a thinner semiconductor chip, for example, to have the semiconductor chip built in a thin card-shape package, and the thickness of the semiconductor chip is reduced to 100 μm or less by further polishing, grinding and etching a rear surface of the semiconductor wafer.
Problems with the cracks when the thickness of the semiconductor chip is thus reduced to 100 μm or less will be described in greater detail referring to FIGS. 24A to 25B.
With the thickness of the semiconductor chip being very small as described above, even if an outer peripheral portion (corner portions in particular) of the semiconductor chip 100 comes off, the semiconductor chip 100 warps in a concave shape before being peeled off as shown in FIG. 24A because a speed at which the PSA tape 101 is peeled off is slower than a speed at which the raising pins 102 are lifted, and is finally cracked as shown in FIG. 24B. Further, as shown in FIG. 25A, if the rear surface side of the semiconductor chip 100 is raised with the raising pins 102 via the PSA tape 101, cracks are caused in portions of the semiconductor chip 100 that contact the raising pins 102 with only the corner portions being peeled off, or the raising pins 102 penetrate, leading to a crack of the chip as shown in FIG. 25B. If the thickness of the semiconductor chip is 100 μm or more, such a phenomenon is less likely to occur since strength (thickness direction) of the semiconductor chip is higher than a force of adhesion to the semiconductor chip 100 of the PSA tape 101.
A conventional manufacturing method of the semiconductor device described above is also applied to a stacked MCP type semiconductor device. In the conventional manufacturing method of stacked MCP type products, semiconductor chips are produced in processes of grinding the rear surface, affixing a film-like adhesive (adhesive layer) onto the rear surface, and dicing, and the plurality of semiconductor chips is stacked on multiple stages by repeating die bonding and bonding, and then molded.
FIGS. 26 to 31 are process sectional views explaining a conventional manufacturing process of the stacked MCP product up to the production of the semiconductor chips. First, a PSA tape (surface protection tape) 24 is affixed to an element formation surface MS of a semiconductor wafer W100 on which a semiconductor element is formed (FIG. 26). The thickness of the semiconductor wafer W100 is then reduced by rear surface grinding (FIG. 27). Further, an adhesive layer 109 for stacking the semiconductor chips is affixed to the rear surface (FIG. 28). Next, the rear surface of the semiconductor wafer W100, opposite to element formation surface MS to which the PSA tape 24 is affixed, is affixed to another PSA tape 112 which is affixed to a wafer ring 102 (FIG. 29). Subsequently, the PSA tape 24 is peeled off (FIG. 30). Next, a semiconductor wafer W100 is separated and cut together with the adhesive layer 109 into semiconductor chips 1 by a laser, a blade or the like (FIG. 31).
The conventional manufacturing method of the semiconductor device described above is also applied to a stacked MCP type semiconductor device. In the conventional manufacturing method of the stacked MCP products, the semiconductor chips are produced in the processes of grinding the rear surface, affixing the film-like adhesive (adhesive layer) onto the rear surface, and dicing, and the plurality of semiconductor chips are stacked on multiple stages by repeating die bonding and bonding, and then molded. This method has the following problems.
(Problem 1) Because the semiconductor chips are produced in the processes of grinding the rear surface, affixing the film-like adhesive and dicing, the rear surface is frequently chipped, so that only the chips with low deflecting strength can be produced. As a result, only the semiconductor chips having a thickness of 100 to 150 μm could be produced.
(Problem 2) Because the rear surface is frequently chipped in the semiconductor chip as described above, the semiconductor chip might be cracked in bonding it.
(Problem 3) A method is conceivable as means to solve the problems described above in which an etching process is performed after the rear surface grinding to enhance the deflecting strength of the chip. However, in this method, the rear surface is more largely chipped than in the method of rear surface grinding followed by dicing without etching if the thickness of the chip is less than 100 μm, and this rather increases plastic defects.
(Problem 4) Even if the problems described above can be solved and the semiconductor chip having thickness less than 100 μm is successfully produced the problems that have been explained referring to FIGS. 24A to 25B still occur.
As described above, if the thickness of the semiconductor chip is reduced, the deflecting strength of the semiconductor chip is decreased. Moreover, quality deterioration such as the cracks and chipping, and a lowering yield ratio can not be avoided with a conventional mechanism and method for peeling the PSA tape and a conventional device and method for picking up the semiconductor chip. Therefore, improvement has been desired in the manufacturing method of the semiconductor device comprising the above. Especially, when the adhesive, and an adhesive layer such as an adhesive sheet or an adhesive film adhere to the rear surface of the semiconductor chip, load is higher during peeling off and fracture is more frequently caused, resulting in a problem of the quality deterioration and lowering yield ratio in the semiconductor device.